High voltage tolerant capacitors

ABSTRACT

A system and method for fabricating on-die metal-insulator-metal capacitors capable of supporting relatively high voltage applications and increasing capacitance per area are described. In various implementations, an integrated circuit includes multiple metal-insulator-metal (MIM) capacitors. The MIM capacitors are formed between two signal nets such as two different power rails, two different control signals, or two different data signals. The integrated circuit includes multiple intermediate metal layers (or metal plates) formed between two signal nets. In high voltage regions, a MIM capacitor has one or more intermediate metal plates formed as floating plates between electrode metal plates. The floating plates have no connection to any power supply reference voltage level used by the integrated circuit. The insulating distance between the two electrode metal plates includes the thicknesses of the two dielectric layers, but the thickness of the conductive floating metal plate does not contribute to this insulating distance.

BACKGROUND Description of the Relevant Art

As both semiconductor manufacturing processes advance and on-diegeometric dimensions reduce, semiconductor chips provide morefunctionality and performance while consuming less space. While manyadvances have been made, design issues still arise with moderntechniques in processing and integrated circuit design that limitpotential benefits. For example, as the number and size of passivecomponents used in a design increase, the area consumed by thesecomponents also increases. Impedance matching circuits, harmonicfilters, decoupling capacitors, bypass capacitors and so on are examplesof these components.

Many manufacturing processes use on-die metal-insulator-metal (MIM)capacitors to provide capacitance in both on-die integrated circuits andoff-chip integrated passive device (IPD) packages. A MIM capacitor isformed with two parallel metal plates separated by a dielectric layer.Generally speaking, each of the two metal plates and the dielectriclayer is parallel to a semiconductor substrate surface. Such MIMcapacitors are used in a variety of integrated circuits, includingoscillators and phase-shift networks in radio frequency (RF) integratedcircuits, as decoupling capacitors to reduce noise in both mixed signalintegrated circuits and microprocessors as well as bypass capacitorsnear active devices in microprocessors to limit the parasiticinductance, and so on. MIM capacitors are also used as memory cells in adynamic RAM.

Fabricating MIM capacitors is a challenging process. The materialselection for the dielectric layer is limited as many of the materialsused for the dielectric layer are able to diffuse with the metal layersused for the parallel metal plates. This limited selection can alsoreduce the capacitance per area that might otherwise be achieved.Further, the on-die region of the integrating circuit using the MIMcapacitor can use a relatively high power supply reference voltagelevel. The MIM capacitor can fail under the high voltage stress, whichcan render the corresponding circuitry unsatisfactory for its intendedpurpose.

In view of the above, efficient methods and systems for fabricatingon-die metal-insulator-metal capacitors capable of supporting relativelyhigh voltage applications and increasing capacitance per area aredesired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a generalized diagram of capacitors of an integrated circuitcapable of supporting relatively high voltage applications andincreasing capacitance per area.

FIG. 2 is a generalized diagram of capacitors of an integrated circuitcapable of supporting relatively high voltage applications andincreasing capacitance per area.

FIG. 3 is a generalized diagram of capacitors of an integrated circuitcapable of supporting relatively high voltage applications andincreasing capacitance per area.

FIG. 4 is a generalized diagram of capacitors of an integrated circuitcapable of supporting relatively high voltage applications andincreasing capacitance per area.

FIG. 5 is a generalized diagram of capacitors of an integrated circuitcapable of supporting relatively high voltage applications andincreasing capacitance per area.

FIG. 6 is a generalized diagram of a method for forming capacitors of anintegrated circuit capable of supporting relatively high voltageapplications and increasing capacitance per area.

FIG. 7 is a generalized diagram of computing system with capacitors ofan integrated circuit capable of supporting relatively high voltageapplications and increasing capacitance per area.

While the invention is susceptible to various modifications andalternative forms, specific implementations are shown by way of examplein the drawings and are herein described in detail. It should beunderstood, however, that drawings and detailed description thereto arenot intended to limit the invention to the particular form disclosed,but on the contrary, the invention is to cover all modifications,equivalents and alternatives falling within the scope of the presentinvention as defined by the appended claims.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the present invention. However, onehaving ordinary skill in the art should recognize that the inventionmight be practiced without these specific details. In some instances,well-known circuits, structures, and techniques have not been shown indetail to avoid obscuring the present invention. Further, it will beappreciated that for simplicity and clarity of illustration, elementsshown in the figures have not necessarily been drawn to scale. Forexample, the dimensions of some of the elements are exaggerated relativeto other elements.

Systems and methods for fabricating on-die metal-insulator-metalcapacitors capable of supporting relatively high voltage applicationsand increasing capacitance per area are contemplated. In variousimplementations, an integrated circuit includes multiplemetal-insulator-metal (MIM) capacitors used in one or more of a varietyof types of circuits. Typically, an on-die capacitor is formed betweentwo signal nets. In some implementations, the two signal nets are powerrails charged to two different voltage levels. For example, a firstsignal net (or first power rail) is charged to a power supply referencevoltage level, and a second signal net (or second power rail) is chargedto a ground reference voltage level. In other implementations, the twosignal nets are two different control signals or two different datasignals used by the on-die integrated circuit.

One or more insulating dielectric layers are formed between the twometal layers used for the first signal net and the second signal net.These one or more insulating dielectric layers include at least oneinter-level dielectric (ILD) layer. The semiconductor fabricationprocess used to create the integrated circuit also supports formingmultiple intermediate metal layers in the ILD between the two signalnets. These intermediate metal layers are used to form capacitor plates.The maximum number of plates formed between the two signal nets is basedon the semiconductor fabrication process used to create the integratedcircuit. For example, the semiconductor fabrication process is capableof supporting three, four, or five intermediate metal layers between twosignal nets. Another number of intermediate metal layers is possible andcontemplated.

The integrated circuit includes one or more regions that are low voltageregions. The low voltage regions include circuitry that uses arelatively low power supply reference voltage level. The integratedcircuit also includes one or more regions that are high voltage regions.The high voltage regions include circuitry that use a relatively highpower supply reference voltage level that is greater than the low powersupply reference voltage level. The MIM capacitors located in the lowvoltage regions of the integrated circuit have each formed intermediatemetal layer (or metal plate) connected to one of the two signal nets.The dielectric layers between the intermediate metal plates are capableof tolerating a potential difference equal to the relatively low powersupply reference voltage level. These dielectric layers are incapable ofsupporting a high voltage stress associated with the potentialdifference equal to the relatively high power supply reference voltagelevel.

In contrast to the low voltage regions, the MIM capacitors located inthe high voltage regions of the integrated circuit have one or moreintermediate metal layers (or metal plates) formed as floating platesbetween electrode metal plates. The floating metal plates have noconnection to any power supply reference voltage level of the integratedcircuit. Between the two electrode metal plates, a MIM capacitor in thehigh voltage region has at least one floating metal plate and at leasttwo dielectric layers. The insulating distance between the two electrodemetal plates includes the thicknesses of the two dielectric layers.However, the thickness of the conductive floating metal plate does notcontribute to this insulating distance. The thicknesses of the twodielectric layers enable the MIM capacitor to tolerate a potentialdifference equal to the relatively high power supply reference voltagelevel and the low power supply reference voltage level. The thickness ofthe conductive floating metal plate reduces this insulating distancefrom a maximum value equal to the distance between the two electrodemetal plates. The corresponding reduction in the insulating distanceincreases the capacitance per unit area of the MIM capacitor.

Turning now to FIG. 1 , a generalized block diagram is shown ofcapacitors 100 of an integrated circuit capable of supporting relativelyhigh voltage applications and increasing capacitance per unit area. Asemiconductor fabrication process forms multiple intermediate metallayers (or metal plates) using metal layer 130 between two signal nets102 and 104. The semiconductor fabrication process uses metal plates toform the high voltage metal-insulator-metal (MIM) capacitors 150 and 160between the two signal nets 102 and 104. The semiconductor fabricationprocess (or process) forms the MIM capacitors 150 and 160 in the oxidelayer 120 between the two signal nets 102 and 104. The process forms anelectrical connection 140 between a particular metal plate and one ofthe two signal nets 102 and 104. The electrical connections 140 includeone of a variety of types of vias. The MIM capacitor 150 (or capacitor150) includes a floating metal plate between two electrode metal plates.The floating plates have no connection to any power supply referencevoltage level used by the integrated circuit.

Although the capacitors 150 and 160 are shown relatively close to oneanother, it is possible that these capacitors are in different regionsof the integrated circuit that use the signal nets 102 and 104. In otherimplementations, the capacitors 150 and 160 do not share the signal nets102 and 104. The capacitors 150 and 160 are shown sharing the signalnets 102 and 104 for ease of illustration. As shown, one electrode metalplate of the capacitor 150 is connected to the signal net 102, whereas,the other electrode metal plate of the capacitor 150 is connected to thesignal net 104. If the middle floating plate of the capacitor 150 wasconnected to one of the signal nets 102 and 104, then the capacitance ofthe capacitor 150 would increase. However, each of the insulatingdistances 152 and 154 is insufficient to tolerate a potential differenceequal to a relatively high power supply reference voltage level. Thecapacitor 150 would fail under the relatively high voltage stress.

The insulating distance 162 of the capacitor 160 is sufficient totolerate the potential difference equal to the relatively high powersupply reference voltage level. However, the insulating distance 162 isalso greater than the sum of the distances 152 and 154. Therefore, thecapacitance per unit area of the capacitor 160 is less than thecapacitance per unit area of the capacitor 150. The capacitor 150 iscapable of supporting relatively high voltage applications while alsoincreasing capacitance per unit area. Further details of thesemiconductor fabrication processing steps used to create the capacitors150 and 160 are provided in a description of method 600 (of FIG. 6 ).However, a brief description is provided in the following discussion.

In an implementation, the two signal nets 102 and 104 have staticvoltage levels over time. In another implementation, the two signal nets102 and 104 have dynamic voltage levels over time. In someimplementations, the two signal nets 102 and 104 are power rails chargedto two different voltage levels. In one example, the signal net 102 ischarged to a power supply reference voltage level, and the second signalnet 104 is charged to a ground reference voltage level. In otherimplementations, the two signal nets 102 and 104 are two differentcontrol signals used by the integrated circuit. In yet otherimplementations, the two signal nets 102 and 104 are two different datasignals used by the integrated circuit.

In one example, the signal net 102 is one signal route using a metalfive (Metal 5, or M5) layer and the signal net 104 is signal route usinga metal four (Metal 4, or M4) layer. For example, a metal zero (Metal 0,or M0) layer of the semiconductor fabrication process is the lowestmetal layer formed above a gate region of a transistor. A metal one(Metal 1, or M1) layer is formed above the metal zero layer, and so on.In some designs, each of the signal nets 102 and 104 use a sameconductive material such as metal layer 110. The metal layer 110 usesone of a variety of conductive materials such as copper, a mixture ofcopper and aluminum, or other. In other designs, the signal net 102 usesa different conductive material than what is used for signal net 104.

Although a single oxide layer 120 is shown as formed between the twometal layers used for the signal net 102 and the signal net 104, in someimplementations, the process forms one or more insulating dielectriclayers. These one or more insulating dielectric layers include at leastone inter-level dielectric (ILD) layer. Each of the insulatingdielectric layers has a particular dielectric constant and a particularthickness. Thicknesses of metal layers and dielectric layers aremeasured in the vertical direction when using the orientation shown inFIG. 1 . For example, the distances 152, 154 and 162 are also referredto as the thicknesses 152, 154 and 162. Using this orientation, thewidths of the metal layers 110 and 130 are measured in a direction goinginto the diagram, whereas, the lengths of the metal layers 110 and 130are measured in the horizontal direction.

The process forms multiple intermediate metal plates that use the metallayer 130 between the two signal nets 102 and 104. The maximum number ofmetal plates formed between the signal nets 102 and 104 is based on thesemiconductor fabrication process used to create the integrated circuit.For example, the semiconductor fabrication process is capable ofsupporting three, four, or five intermediate metal plates between thesignal nets 102 and 104. Another number of intermediate metal plates isalso possible and contemplated. In some designs, each of the metalplates uses a same conductive material such as metal layer 130. In animplementation, the metal layer 130 is one of tantalum nitride (TaN) andtitanium nitride (TiN) in contrast to copper or a copper and aluminummixture. In other implementations, the metal layer 130 uses copper, amixture of copper and aluminum, or other. In other designs, one or moreof the metal plates use a different conductive material than what isused for other metal plates between the signal nets 102 and 104.Similarly, in some designs, each of the metal plates uses a samethickness, whereas, in other designs, one or more of the metal platesuse a different thickness than what is used for other metal plates.

To increase yield and increase rigidity of the dies of the wafers, insome implementations, the process creates a maximum number of metalplates in particular regions even when the metal plates are not used. Insome designs, the maximum number of metal plates is three as shown incapacitors 100. The capacitor 150 uses each of the three available metalplates although the middle metal plate is a floating plate. In otherdesigns, the process supports skipping the forming of unused metalplates. The capacitor 160 uses two metal plates by skipping the middlemetal plate. Although the capacitor 150 is shown to include a singlefloating metal plate, in other implementations, the capacitor 150includes two or more floating metal plates between the electrode metalplates when the process supports forming more than three metal plates.

Turning now to FIG. 2 , a generalized block diagram is shown ofcapacitors 200 of an integrated circuit capable of supporting relativelyhigh voltage applications and increasing capacitance per unit area.Signals and materials described earlier are numbered identically. Thecapacitors 200 includes the high voltage capacitor 150 and the lowvoltage capacitor 210. The capacitor 150 is connected to the signal net102, which provides a relatively high power supply reference voltagelevel. The capacitor 210 is connected to the signal net 106, whichprovides a relatively low power supply reference voltage level. Thesignal net 106 is physically and electrically separated from the signalnet 102 although the signal net 106 is formed with a same metal layer asthe signal net 102. In one example, each of the signal nets 102 and 106uses a metal five (M5) layer. Similar to the signal net 102, the signalnet 106 is one of a power rail used by the integrated circuit, a controlsignal used by the integrated circuit, and a data signal used by theintegrated circuit. Although it is shown that each of the capacitors 150and 210 share the signal net 104, in other implementations, thecapacitors 150 and 210 are connected to different signal nets. However,in each implementation, the potential difference across the capacitor150 is appreciably greater than the potential difference across thecapacitor 210. Similar to the capacitor 150, the capacitor 210 includesthree metal plates between the two signal nets. The capacitor 210 useseach of the three metal plates as electrode metal plates. The top andbottom metal plates of the capacitor 210 are connected to the signal net104. The middle metal plate is connected to the signal net 102.

The equivalent capacitance of capacitor 210 is a sum of the capacitancesof the first capacitance that uses the insulating distance 212 and thesecond capacitance that uses the insulating distance 214. These twocapacitances of the capacitor 210 are connected in a parallelconfiguration. The first capacitance includes the ratio of the overlaparea of the top metal plate and the middle metal plate to the insulatingdistance 212. The dielectric constant of the dielectric material, suchas oxide layer 120, between the two metal plates also affects thecapacitance. Similarly, the second capacitance includes the ratio of theoverlap area of the middle metal plate and the bottom metal plate to theinsulating distance 214. The dielectric constant of the dielectricmaterial, such as oxide layer 120, between the two metal plates alsoaffects the capacitance.

The equivalent capacitance of capacitor 210 is greater than the totalcapacitance of capacitor 150. The capacitance of capacitor 150 includesthe ratio of the overlap area of the top metal plate and the bottommetal plate to the sum of the insulating distances 152 and 154. Thedielectric constant of the dielectric material should be the same asused for the capacitor 210. Therefore, the insulating distance betweenthe two electrode metal plates of capacitor 150 includes the thicknessesof the two dielectric layers such as distances 152 and 154. However, thethickness of the conductive floating metal plate does not contribute tothis insulating distance. Although the capacitor 150 provides lesscapacitance than capacitor 210, the capacitor 150 tolerates highervoltage stress. Without using a different dielectric material with adifferent dielectric constant and without changing the semiconductorfabrication process, the capacitor 150 provides a high voltagecapacitor. By utilizing the floating metal plate, the capacitor 150provides reliability for high voltage applications without addingadditional manufacturing cost.

Referring to FIG. 3 , a generalized block diagram is shown of capacitors300 of an integrated circuit capable of supporting relatively highvoltage applications and increasing capacitance per unit area. Signalsand materials described earlier are numbered identically. The capacitors300 includes the high voltage capacitors 310 and 320. Here, in thisexample, the semiconductor fabrication process supports forming at leastfive metal plates between the two signal nets 102 and 104. The capacitor310 includes three floating metal plates between electrode metal plates.The capacitor 320 includes two floating metal plates between electrodemetal plates.

The capacitance of capacitor 310 includes the ratio of the overlap areaof the top metal plate adjacent to signal net 102 and the bottom metalplate adjacent to signal net 104 to the sum of the insulating distances312, 314, 316 and 318. Therefore, the insulating distance between thetwo electrode metal plates of capacitor 310 excludes the thicknesses ofthe three floating metal plates between the two electrode metal plates.The capacitance of capacitor 320 includes the ratio of the overlap areaof the second metal plate from the signal net 102 and the bottom metalplate adjacent to signal net 104 to the sum of the insulating distances322, 324 and 326. The floating metal plate adjacent to the signal net102 does not contribute to the capacitance of capacitor 320. Theinsulating distance between the two electrode metal plates of capacitor320 excludes the thicknesses of the two floating metal plates betweenthe two electrode metal plates.

The sum of the distances 324, 326 and 328 is less than the sum of thedistances 312, 314, 316 and 318. Therefore, the capacitance of capacitor320 is greater than the capacitance of capacitor 310. Using the samedimensions, each of the capacitors 310 and 320 has a smaller capacitancethan the capacitor 150 (of FIGS. 1-2 ). However, each of the capacitors310 and 320 is able to tolerate a greater potential difference betweenthe electrode metal plates than the capacitor 150.

Referring to FIG. 4 , a generalized block diagram is shown of capacitors400 of an integrated circuit capable of supporting relatively highvoltage applications and increasing capacitance per unit area. Signalsand materials described earlier are numbered identically. The capacitors400 includes the high voltage capacitor 410 and the low voltagecapacitor 420. Here, in this example, the semiconductor fabricationprocess supports forming at least five metal plates between the twosignal nets 102 and 104 and between the two signal nets 106 and 104. Thecapacitor 410 includes one floating metal plate between electrode metalplates. The capacitor 420 includes four capacitors connected in aparallel configuration, and each capacitor has no floating metal platebetween electrode metal plates.

The capacitance of capacitor 410 includes the ratio of the overlap areaof the electrode metal plates, such as the middle metal plate and thebottom metal plate, to the sum of the insulating distances 412 and 414.The insulating distance between the two electrode metal plates ofcapacitor 410 excludes the thickness of the floating metal plate betweenthe two electrode metal plates. The two floating metal plates locatednear the signal net 102 do not contribute to the capacitance ofcapacitor 410.

The equivalent capacitance of capacitor 420 is a sum of the capacitancesof the four capacitances that use the insulating distances 422, 424, 426and 428. These four capacitances of the capacitor 420 are connected in aparallel configuration. The first capacitance includes the ratio of theoverlap area of the top metal plate and the adjacent metal plate to theinsulating distance 422. The second capacitance includes the ratio ofthe overlap area of the second metal plate from the top and the middlemetal plate to the insulating distance 424. The third capacitance andthe fourth capacitance are determined in a similar manner using theinsulating distances (thicknesses) 426 and 428. The capacitance ofcapacitor 420 is greater than the capacitance of capacitor 410. However,the capacitor 410 is able to tolerate a greater potential differencebetween the electrode metal plates than the capacitor 420.

Referring to FIG. 5 , a generalized block diagram is shown of capacitors500 of an integrated circuit capable of supporting relatively highvoltage applications and increasing capacitance per unit area. Signalsand materials described earlier are numbered identically. The capacitors500 includes the high voltage capacitor 510 and the low voltagecapacitor 420. Here, in this example, the semiconductor fabricationprocess supports forming at least five metal plates between the twosignal nets 102 and 104 and between the two signal nets 106 and 104. Thecapacitor 510 includes two floating metal plates between electrode metalplates.

The capacitance of capacitor 510 includes the ratio of the overlap areaof the electrode metal plates, such as the middle metal plate and thebottom metal plate, to the sum of the insulating distances (thicknesses)512, 514 and 516. The insulating distance between the two electrodemetal plates of capacitor 510 excludes the thickness of the two floatingmetal plates between the two electrode metal plates. The floating metalplates located at the bottom adjacent to the signal net 104 does notcontribute to the capacitance of capacitor 510. The capacitance ofcapacitor 420 is greater than the capacitance of capacitor 510. However,the capacitor 510 is able to tolerate a greater potential differencebetween the electrode metal plates than the capacitor 420. When usingthe same dimensions, the capacitance of capacitor 510 is also less thanthe capacitance of capacitance of capacitor 410 (of FIG. 4 ). Forexample, the sum of the insulating distances (thicknesses) 512, 514 and516 is greater than the sum of the insulating distances (thicknesses)412 and 414. However, the capacitor 510 is able to tolerate a greaterpotential difference between the electrode metal plates than thecapacitor 410 although the capacitor 410 is also a high voltagecapacitor.

Turning to FIG. 6 , a generalized block diagram of a method 600 forforming capacitors of an integrated circuit capable of supportingrelatively high voltage applications and increasing capacitance per areais shown. For purposes of discussion, the steps in this implementationare shown in sequential order. However, in other implementations somesteps occur in a different order than shown, some steps are performedconcurrently, some steps are combined with other steps, and some stepsare absent. Typically, an on-die capacitor is formed between two signalnets. In some implementations, the two signal nets are power railscharged to two different voltage levels. A first signal net (or firstpower rail) is charged to a power supply reference voltage level, and asecond signal net (or second power rail) is charged to a groundreference voltage level. In other implementations, the two signal netsare two different control signals or two different data signals used bythe on-die integrated circuit. In one example, the first signal net is ametal four (M4) layer and the second signal net is a metal five (M5)layer. In one example, the first signal net is equivalent to the signalnet 104 and the second signal net is equivalent to the signal net 102(of FIGS. 1-5 ). One or more insulating dielectric layers are formedbetween the two metal layers used for the first signal net and thesecond signal net. These one or more insulating dielectric layersinclude at least one inter-level dielectric (ILD). A semiconductorfabrication process (or process) forms, in an integrated circuit, thefirst signal net that uses an on-die capacitor with another signal net(block 602).

To form the first signal net, the process forms a metal layer on top ofan oxide layer, such as the inter-level dielectric (ILD). The ILD isused to insulate metal layers, which are used for interconnects. In someimplementations, the ILD is silicon dioxide. In other implementations,the ILD is one of a variety of low-k dielectrics containing carbon orfluorine. The low-k dielectrics provide a lower capacitance between themetal layers, and thus, reduce performance loss, power consumption, andcross talk between interconnect routes. A chemical mechanicalplanarization (CMP) step is used to remove unwanted ILD and to polishthe remaining ILD. The CMP step achieves a near-perfect flat and smoothsurface upon which further layers are built. Following, the processdeposits the metal layer to be used as the first signal net. The metallayer is one of a variety of conductive materials such as copper, amixture of copper and aluminum, and so on.

In some implementations, the process uses a dual damascene process toform the metal layer of the first signal net, whereas, in otherimplementations, the process uses a single damascene process. These andother techniques are contemplated. When the process uses copper for thefirst signal net, the process deposits a liner on the ILD before formingthe metal layer. The liner uses a tantalum (Ta) based barrier materialto prevent the copper from diffusing into the ILD and to act as anadhesion layer for the copper. Next, the process deposits a thin copperseed layer by physical vapor diffusion (PVD) followed by electroplatingof copper. Afterward, the process polishes the excess copper metal anddeposits a capping layer typically SiN (silicon mononitride). Theprocess forms an additional oxide layer on top of the first signal netof a controlled thickness. In various implementations, the thickness ofthe oxide layer on top of the first signal net is at least an order ofmagnitude greater than a thickness of a thin gate silicon dioxide layerformed for active devices such as transistors. The process deposits theoxide layer using a combination of gasses such as dichlorosilane orsilane with oxygen precursors, such as oxygen and nitrous oxide,typically at pressures from a few millitorr to a few torr.

The process forms a first metal layer to be used as a first plate of theon-die capacitor (block 604). The process uses one of a variety ofconductive materials and methods to form the first metal layer asdescribed earlier. In some implementations, the process uses a sameconductive material for the first metal layer as used for the firstsignal net, whereas, in other implementations, the first signal net andthe first metal layer use different conductive materials. For example,in some implementations, the first metal layer is one of tantalumnitride (TaN) and titanium nitride (TiN) in contrast to copper or acopper and aluminum mixture. In such implementations, the process formsthe first metal layer using atomic layer deposition (ALD), or physicalvapor deposition (PVD) such as a sputter technique.

The process forms a first dielectric layer adjacent to the first metallayer (block 606). In an implementation, the process uses an atomiclayer deposition to form a relatively high-K oxide dielectric on thefirst metal layer. The process forms a second metal layer as a floatingplate adjacent to the first dielectric layer (block 608). The processdeposits the second metal layer on top of the first dielectric layer,and forms (deposits) a second dielectric layer adjacent to the secondmetal layer (block 610). The second metal layer that is used as afloating plate has no connection to a voltage reference level used bythe integrated circuit. The process uses similar techniques as describedearlier to form the second metal layer and the second dielectric layer.In some implementations, the process uses a same conductive material forthe second metal layer as used for the first metal layer, whereas, inother implementations, the first metal layer and the second metal layeruse different conductive materials. Similarly, in some implementations,the process uses a same insulating material for the second dielectriclayer as used for the first dielectric layer, whereas, in otherimplementations, the first dielectric layer and the second dielectriclayer use different insulating materials.

The process forms a third metal layer adjacent to the second dielectriclayer creating a metal-insulator-metal (MIM) capacitor of the integratedcircuit between the first metal layer and the third metal layer (block612). The conductive material of the third metal layer is the sameconductive material used for one of the first signal net, the firstmetal layer, and the second metal layer. Alternatively, the process usesa different conductive material. The MIM capacitor has two dielectriclayers with the second metal layer in the middle separating the twodielectric layers. The second metal layer is also a floating plate.

Each of these layers of the MIM capacitor has a thickness. In someimplementations, one or more of the layers have a same thickness asanother layer. For example, in an implementation, the first metal layerand the third metal layer have a same thickness, and the firstdielectric layer and the second dielectric layer have a same thickness.In another implementation, each of the layers has a unique, respectivethickness. The thickness of the second metal layer reduces theinsulating distance between the first metal layer and the third metallayer. The reduced insulating distance increases the capacitance of theMIM capacitor.

The process forms a second signal net that uses the on-die capacitorwith the first signal net (block 614). The process uses similartechniques described earlier for forming the first signal net and itscorresponding ILD. The process forms one of a variety of via types tophysically connect the first signal net to the first metal layer, and tophysically connect the third metal layer to the second signal net.Therefore, each of the first metal layer and the third metal layerreceives a respective voltage reference level applied to the firstsignal net and the second signal net (block 616).

If a potential is not applied to an input node of the integrated circuit(“no” branch of the conditional block 618), then the integrated circuitwaits for power up (block 620). However, if a potential is applied tothe input node of the integrated circuit (“yes” branch of theconditional block 618), then the circuitry of the integrated circuitconveys a current from the input node to an output node of theintegrated circuit while charging the MIM capacitor (block 622).

Referring to FIG. 7 , one implementation of a computing system 700 isshown. The computing system 700 includes the processor 710 and thememory 730. Interfaces, such as a memory controller, a bus or acommunication fabric, one or more phased locked loops (PLLs) and otherclock generation circuitry, a power management unit, and so forth, arenot shown for ease of illustration. It is understood that in otherimplementations, the computing system 700 includes one or more of otherprocessors of a same type or a different type than processor 710, one ormore peripheral devices, a network interface, one or more other memorydevices, and so forth. In some implementations, the functionality of thecomputing system 700 is incorporated on a system on chip (SoC). In otherimplementations, the functionality of the computing system 700 isincorporated on a peripheral card inserted in a motherboard. Thecomputing system 700 is used in any of a variety of computing devicessuch as a server computer, a desktop computer, a tablet computer, alaptop, a smartphone, a smartwatch, a gaming console, a personalassistant device, and so forth.

The processor 710 includes hardware such as circuitry. For example, theprocessor 710 includes at least one integrated circuit 720, whichutilizes MIM capacitors 722. The integrated circuit 720 uses the MIMcapacitors 722 for a variety of applications such as decoupling twosignal nets from one another, smoothing or stabilizing the current andvoltage output of power supplies and voltage regulators, adjustingfrequency tuning circuitry, reconstructing receiving signals fromtransmission lines, and so on. Other examples of applications that usethe MIM capacitors 722 are oscillators and phase-shift networks in radiofrequency (RF) integrated circuits, bypass capacitors near activedevices in microprocessors to limit the parasitic inductance, memorycell data storage in dynamic RAM, and so on. The MIM capacitors 722 arecapable of supporting relatively high voltage applications andincreasing capacitance per area. For example, one or more of the MIMcapacitors 722 instantiated in the integrated circuit 720 useconfigurations as shown earlier for capacitors 100-500 (of FIGS. 1-5 ).

In various implementations, the processor 710 includes one or moreprocessing units. In some implementations, each of the processing unitsincludes one or more processor cores capable of general-purpose dataprocessing, and an associated cache memory subsystem. In such animplementation, the processor 710 is a central processing unit (CPU). Inanother implementation, the processing cores are compute units, eachwith a highly parallel data microarchitecture with multiple parallelexecution lanes and an associated data storage buffer. In such animplementation, the processor 710 is a graphics processing unit (GPU), adigital signal processor (DSP), or other.

In some implementations, the memory 730 includes one or more of a harddisk drive, a solid-state disk, other types of flash memory, a portablesolid-state drive, a tape drive and so on. The memory 730 stores anoperating system (OS) 732, one or more applications represented by code734, and at least source data 736. Memory 730 is also capable of storingintermediate result data and final result data generated by theprocessor 710 when executing a particular application of code 734.Although a single operating system 732 and a single instance of code 734and source data 736 are shown, in other implementations, another numberof these software components are stored in memory 730. The operatingsystem 732 includes instructions for initiating the boot up of theprocessor 710, assigning tasks to hardware circuitry, managing resourcesof the computing system 700 and hosting one or more virtualenvironments.

Each of the processor 710 and the memory 730 includes an interface unitfor communicating with one another as well as any other hardwarecomponents included in the computing system 700. The interface unitsinclude queues for servicing memory requests and memory responses, andcontrol circuitry for communicating with one another based on particularcommunication protocols. The communication protocols determine a varietyof parameters such as supply voltage levels, power-performance statesthat determine an operating supply voltage and an operating clockfrequency, a data rate, one or more burst modes, and so on.

It is noted that one or more of the above-described implementationsinclude software. In such implementations, the program instructions thatimplement the methods and/or mechanisms are conveyed or stored on acomputer readable medium. Numerous types of media which are configuredto store program instructions are available and include hard disks,floppy disks, CD-ROM, DVD, flash memory, Programmable ROMs (PROM),random access memory (RAM), and various other forms of volatile ornon-volatile storage.

Generally speaking, a computer accessible storage medium includes anystorage media accessible by a computer during use to provideinstructions and/or data to the computer. For example, a computeraccessible storage medium includes storage media such as magnetic oroptical media, e.g., disk (fixed or removable), tape, CD-ROM, orDVD-ROM, CD-R, CD-RW, DVD-R, DVD-RW, or Blu-Ray. Storage media furtherincludes volatile or non-volatile memory media such as RAM (e.g.synchronous dynamic RAM (SDRAM), double data rate (DDR, DDR2, DDR3,etc.) SDRAM, low-power DDR (LPDDR2, etc.) SDRAM, Rambus DRAM (RDRAM),static RAM (SRAM), etc.), ROM, Flash memory, non-volatile memory (e.g.Flash memory) accessible via a peripheral interface such as theUniversal Serial Bus (USB) interface, etc. Storage media includesmicroelectromechanical systems (MEMS), as well as storage mediaaccessible via a communication medium such as a network and/or awireless link.

Additionally, in various implementations, program instructions includebehavioral-level descriptions or register-transfer level (RTL)descriptions of the hardware functionality in a high level programminglanguage such as C, or a design language (HDL) such as Verilog, VHDL, ordatabase format such as GDS II stream format (GDSII). In some cases thedescription is read by a synthesis tool, which synthesizes thedescription to produce a netlist including a list of gates from asynthesis library. The netlist includes a set of gates, which alsorepresent the functionality of the hardware including the system. Thenetlist is then placed and routed to produce a data set describinggeometric shapes to be applied to masks. The masks are then used invarious semiconductor fabrication steps to produce a semiconductorcircuit or circuits corresponding to the system. Alternatively, theinstructions on the computer accessible storage medium are the netlist(with or without the synthesis library) or the data set, as desired.Additionally, the instructions are utilized for purposes of emulation bya hardware based type emulator from such vendors as Cadence®, EVE®, andMentor Graphics®.

Although the implementations above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. An integrated circuit comprising: a first metallayer; a first dielectric layer adjacent to the first metal layer; asecond metal layer adjacent to the first dielectric layer; a seconddielectric layer adjacent to the second metal layer; and a third metallayer adjacent to the second dielectric layer, wherein ametal-insulator-metal (MIM) capacitor is formed between the first metallayer and the third metal layer; and wherein: each of the first metallayer and the third metal layer is connected to a respective voltagereference level with one of the respective voltage reference levelsbeing a first power supply voltage reference level that is differentfrom a second power supply voltage level used in another region of theintegrated circuit; and the second metal layer is a floating net with noconnection to a voltage reference level used by the integrated circuit.2. The integrated circuit as recited in claim 1, further comprising oneor more metal layers in addition to the second metal layer between thefirst metal layer and the third metal layer that are floating with noconnection to a voltage reference level used by the integrated circuit.3. The integrated circuit as recited in claim 1, wherein the first metallayer is connected, via a fourth metal layer, to a first signal net thatuses the first power supply voltage reference level.
 4. The integratedcircuit as recited in claim 3, wherein: the third metal layer isconnected to a second signal net via a fifth metal layer; and the fourthmetal layer and the fifth metal layer are adjacent signal metal layers.5. The integrated circuit as recited in claim 4, wherein the first metallayer, the second metal layer and the third metal layer are metal layersbetween adjacent signal metal layers.
 6. The integrated circuit asrecited in claim 1, further comprising one or more metal layers betweenthe first metal layer and a fourth metal layer that are floating with noconnection to a voltage reference level used by the integrated circuit.7. The integrated circuit as recited in claim 1, wherein: each of thefirst dielectric layer and the second dielectric layer comprises a givenoxide layer; and the given oxide layer comprises an oxide layersurrounding the first metal layer, the second metal layer, and the thirdmetal layer.
 8. A method for fabricating an integrated circuitcomprising: forming a first metal layer; forming a first dielectriclayer adjacent to the first metal layer; forming a second metal layeradjacent to the first dielectric layer; forming a second dielectriclayer adjacent to the second metal layer; and forming a third metallayer adjacent to the second dielectric layer, wherein ametal-insulator-metal (MIM) capacitor of an integrated circuit is formedbetween the first metal layer and the third metal layer; and receiving arespective voltage reference level by each of the first metal layer andthe third metal layer with one of the respective voltage referencelevels being a first power supply voltage reference level that isdifferent from a second power supply voltage level used in anotherregion of the integrated circuit; and wherein the second metal layer isa floating net with no connection to a voltage reference level used bythe integrated circuit.
 9. The method as recited in claim 8, furthercomprising receiving, by one or more metal layers in addition to thesecond metal layer between the first metal layer and the third metallayer, no voltage reference level used by the integrated circuit. 10.The method as recited in claim 8, further comprising receiving, by thefirst metal layer via a fourth metal layer, a first signal net that usesthe first power supply voltage reference level.
 11. The method asrecited in claim 10, further comprising: receiving, by the second metallayer, a second signal net via a fifth metal layer; and placing thefourth metal layer and the fifth metal layer as adjacent signal metallayers.
 12. The method as recited in claim 10, further comprisingplacing the first metal layer, the second metal layer and the thirdmetal layer as metal layers between adjacent signal metal layers. 13.The method as recited in claim 8, further comprising forming one or moremetal layers between the first metal layer and a fourth metal layer thatare floating with no connection to a voltage reference level used by theintegrated circuit.
 14. The method as recited in claim 13, furthercomprising forming each of the first dielectric layer and the seconddielectric layer as a given oxide layer, wherein the given oxide layercomprises an oxide layer surrounding the first metal layer, the secondmetal layer, and the third metal layer.